Conventionally, images such as tone images and mono-tone images including characters and symbols have been formed on a substrate through a thermal transfer system. With respect to the thermal transfer system, a heat-sensitive sublimation transfer system and a heat-sensitive melt transfer system have been widely used.
Of these systems, in the heat-sensitive sublimation transfer system, a thermal transfer film formed by supporting a dye layer made by melting or dispersing a sublimable dye serving as a colorant in a binder resin on a substrate is used, and with this thermal transfer film being superposed on an image-receiving film, energy is applied to a heating device such as a thermal head in accordance with image information so that the sublimable dye contained in the dye layer on the thermal transfer film is transferred to the image-receiving film to form an image thereon.
This heat-sensitive sublimation transfer system makes it possible to control the amount of dye transfer on a dot basis in response to the quantity of energy to be applied to the thermal transfer film; therefore, this system has the advantages of forming a superior tone image and of easily forming characters, symbols and the like.
In the image formed by the heat-sensitive sublimation transfer system, since the transferred dye is present on the surface of the image-receiving member, various techniques have been proposed to protect the image and to form a protective layer on the image from the viewpoints of image protection such as light resistance and abrasion resistance (for example, see Patent Document 1 and Patent Document 2).
However, among the printed articles sublimation-transferred, some of the printed articles call for a proper stamping property for use in water based type stamps (for example, printed articles used for certificate photographs such as passports). In other words, a proper fixing property for water based ink is required.
From the viewpoint of fixing property for water based ink, for example, in the field of ink-jet receiving layers, an ink-jet receiving layer in which the outermost surface layer is made of a water-absorbing resin such as polyvinyl alcohol (PVA) containing a large amount of particles such as silica has been known. However, the ink-jet receiving layer of this type is applied with a considerable amount of coating material (normally, 10 g/m2 or more) so as to maintain a sufficient water based ink fixing property. Consequently, even in an attempt to utilize such a receiving layer as a protective layer for a printed article formed through the thermal transfer system, problems arise in which: the foil-separating property is poor and the transparency of the film becomes insufficient. With respect to the protective layer for a printed image formed through the thermal transfer system, a proper fixing property for water based stamp is required in addition to the thin-film and transparent properties; therefore, the techniques for the ink-jet receiving layer are hardly applied to the protective layer for a protective layer thermal transfer film.
Moreover, with respect to the protective layer of a printed article formed through the thermal transfer system such as a sublimation transfer system, a property that is contradictory to the water based ink fixing property, that is, a water-resistant property (by which no problem is raised even when wiped after having been moistened with water), is also required.
In the case where the protective layer is formed by using a water-absorbing resin so as to obtain a proper stamping property and the like, since the protective layer thermal transfer film has a peeling interface formed by using the water-absorbing resin, the corresponding film or sheet tends to be easily influenced by humidity, resulting in a change in the adhesion of the peeling interface and the subsequent problem of an insufficient peeling property. In particular, this problem becomes conspicuous before and after preservation under a high-temperature and high-humidity environment.
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-80844
Patent Document 2: Japanese Patent Application Laid-Open No. 2000-71626